Topographical models of geographical areas may be used for many applications. For example, topographical models may be used in flight simulators and other planning missions. Furthermore, topographical models of man-made structures, for example, cities, may be extremely helpful in applications, such as, cellular antenna placement, urban planning, disaster preparedness and analysis, and mapping.
Various types of topographical models are presently being used. One common topographical model is the digital elevation model (DEM). A DEM is a sampled matrix representation of a geographical area, which may be generated in an automated fashion by a computer. In a DEM, coordinate points are made to correspond with a height value. DEMs are typically used for modeling terrain where the transitions between different elevations, for example, valleys, mountains, are generally smooth from one to a next. That is, a basic DEM typically models terrain as a plurality of curved surfaces and any discontinuities therebetween are thus “smoothed” over. Another common topographical model is the digital surface model (DSM). The DSM is similar the DEM but may be considered as further including details regarding buildings, vegetation, and roads in addition to information relating to terrain.
One particularly advantageous 3D site modeling product is RealSite® from the Harris Corporation of Melbourne, Fla. (Harris Corp.), the assignee of the present application. RealSite® may be used to register overlapping images of a geographical area of interest and extract high resolution DEMs or DSMs using stereo and nadir view techniques. RealSite® provides a semi-automated process for making three-dimensional (3D) topographical models of geographical areas, including cities, that have accurate textures and structure boundaries. Moreover, RealSite® models are geospatially accurate. That is, the location of any given point within the model corresponds to an actual location in the geographical area with very high accuracy. The data used to generate RealSite® models may include aerial and satellite photography, electro-optical, infrared, and light detection and ranging (LIDAR), for example.
Another similar system from the Harris Corp. is LiteSite®. LiteSite® models provide automatic extraction of ground, foliage, and urban digital elevation models (DEMs) from LIDAR and synthetic aperture radar (SAR)/interfermetric SAR (IFSAR) imagery. LiteSite® can be used to produce affordable, geospatially accurate, high-resolution 3-D models of buildings and terrain.
U.S. Pat. No. 6,654,690 to Rahmes et al., which is also assigned to the present assignee and is hereby incorporated herein in its entirety by reference, discloses an automated method for making a topographical model of an area including terrain and buildings thereon based upon randomly spaced data of elevation versus position. The method includes processing the randomly spaced data to generate gridded data of elevation versus position conforming to a predetermined position grid, processing the gridded data to distinguish building data from terrain data, and performing polygon extraction for the building data to make the topographical model of the area including terrain and buildings thereon.
Although stereographic generation of DSMs using the overlapping images of a geographical area of interest may produce detailed results, there may be some potential drawbacks. For example, each image has associated geolocation data, i.e. the geolocation of the image. Although the images may be detailed, the geolocation data may have an undesirable low accuracy. Indeed, once the images are stereographically processed to provide a DSM, the accuracy may further deteriorate, which may be undesirable in applications that depend on detailed DSMs.
An approach to georeferencing images of geographical areas is disclosed in U.S. Patent Application Publication No. 2008/0089558 to Vadon et al. This method includes producing of a digital relief form, from a pair of digital images, and processing the intermediate digital relief form and the reference digital form by calculating the position offsets between the points of the digital reference relief form and their equivalents in the intermediate digital relief form with a view to refining the picture model of the digital image to be georeferenced. The method also includes generating a digital relief form, called the final digital relief form, from the pair of digital images and from the refined picture model, and projecting the final digital relief form and the digital image on the ground, in a geographical or cartographic system.